Diamino-dicyclohexyl methane (H12MDA) comprises isomers such as 4,4′-diamino-dicyclohexyl methane (4,4′-H12MDA), 2,4′-diamino-dicyclohexyl methane (2,4′-H12MDA), 2,2′-diamino-dicyclohexyl methane (2,2′-H12MDA), etc. 4,4′-H12MDA is primarily used for preparing a new generation of high performance anti-aging polyurethane dicyclohexyl methane diisocyanate (H12MDI), which is suitable for preparing lightweight, stable performance of polyurethane coatings and paints. 4,4′-H12MDA is also used as the amine component of the curing agent of epoxy resin and transparent nylon. 4,4′-H12MDA comprises three types, i.e., trans-trans-, trans-cis-, cis-cis-, of isomers, referred simply to as trans-trans-isomer, trans-cis-isomer, cis-cis-isomer correspondingly.
Diamino-diphenyl methane (MDA) comprises isomers such as 4,4′-diamino-diphenyl methane (4,4′-MDA), 2,4′-diamino-diphenyl methane (2,4′-MDA), 2,2′-diamino-diphenyl methane (2,2′-MDA), etc. 4,4′-MDA is very difficult to be hydrogenated due to the stability and the steric hindrance of the aromatic ring. In most of the patents relating to catalytic hydrogenation of 4,4′-MDA, the catalytic reaction is conducted intermittently in a stirred tank reactor or fixed bed reactor at high temperature and high pressure by using a supported noble metal catalyst, in order to obtain a satisfactory yield and a suitable proportion of the trans-trans-isomer.
EP0231788 disclosed an improved batch hydrogenation process of 4,4′-MDA, which prepares 4,4′-H12MDA having the trans-trans-isomer content of 17-24 wt % by using THF solvent and two component catalyst of rhodium and ruthenium at 170-195° C. and 700-1500 psig. Said patent did not provide a technical solution for restoring the catalytic activity by treating the catalyst using a certain technical means when the performance of the catalyst is reduced due to long time use.
The continuous production of 4,4′-H12MDA is also mentioned in patent literatures. US20020198409 disclosed a process for the continuous reduction of 4,4′-MDA, wherein a powdered supported ruthenium catalyst having ruthenium metal content of 1-10% and powder micropore diameter of 5-150 μm is used to catalyze the reaction at the conditions of 130-200° C. and 50-400 bar in the reaction system having water content of less than 1% and alcohols used as the solvent in a series of suspension reactors consisting of continuous bubble columns. When the catalyst activity is decreased, it need to shut down the reaction system to clean the catalyst, which results in rise of the costs and is unfavourable for continuous production.
U.S. Pat. No. 5,196,594 disclosed a process for reducing 4,4′-MDA or the mixture of 2,4′-MDA, 2,2′-MDA and 4,4′-MDA by continuous hydrogenation, which prepares 4,4′-H12MDA having the trans-trans isomer content of 18.5-23.5 wt % by using a supported ruthenium as the catalyst at 100-190° C. and 50-350 bar in at least one fixed bed reactor, wherein the support has BET specific area of about 70-280 m2/g and average pore diameter of 10-320 Å. After 360 h of run, the yield of H12MDA can still reach 93.7%, but the amount of the feed per hour processed by the catalyst is only 0.04-0.1 Kg MDA/Kg Cat, and it did not mention the method of regenerating the catalyst after deactivation of the catalyst.
In the continuous production of 4,4′-HMDA, the catalytic activity, selectivity and the like are reduced after long term run of the catalyst. The above-said patents did not mention the real-time regeneration of the catalyst during the continuous reaction. U.S. Pat. No. 3,071,551 disclosed a process of regenerating a rhodium catalyst by heating, but the process needs to discharge the catalyst and increase corresponding equipments to achieve the purpose, and thus it is very difficult to implement the process whether for batch mode or continuous mode. U.S. Pat. No. 3,856,862 disclosed a process for regenerating catalyst by a separate regenerating system, wherein the catalyst is regenerated by heating at high temperature in the presence of oxygen used as oxidizing agent in a special tubular reactor. Similarly, the technical solution needs to discharge the catalyst and to provide a special equipment to achieve regeneration of the catalyst.
There are the following drawbacks in the prior art:
1) The catalyst productivity is low, and the amount of the feed processed per hour by the catalyst is only 0.04-0.1 Kg MDA/Kg Cat.
2) When the activity of the catalyst is decreased, it needs to shut down the production system, and a separate equipment is required to regenerate the catalyst, which increases the investment costs and is unfavorable for continuous production.